Over the past several years there have been rapid improvements in hardware and software technologies for 3D printing, known more generally as additive manufacturing. This has led to a wide range of applications in both industry and research where parts can be designed and printed as needed. The use of 3D printing provides several benefits in comparison to traditional manufacturing methods, most notably greater design freedom, allowing the fabrication of complex architectures previously unattainable through standard machining. This allows for computationally optimized designs in which parts can be enhanced to achieve lower densities as well as unique mechanical and structural properties. The declining cost and greater accessibility of 3D printing technology has tremendous potential for future development toward novel functional materials
Direct metal 3D printing has become a popular manufacturing technique for rapidly fabricating parts that require the structural, thermal, or electrical functionality of a metal. While useful in many applications, the selective laser melting (SLM) process by which metal structures are formed has several inherent limitations. SLM relies on the melting of metal powder beds composed of dispersed particles with diameters typically in the tens of μm. The localized melting process is very complex, involving large temperature gradients. Spatial resolution in these systems is limited by a combination of particle size and heat transport mechanisms, making the reliable printing of sub-millimeter features very difficult. Also, the process can generate voids, impurities, and other defects that compromise the properties of small scale features. Additionally, the relatively high cost of printing precious metals such as platinum, palladium, or gold may be prohibitive for applications where only surface functionality is needed.
In contrast to metal 3D printing, polymer printing techniques such as automatic extruding (e.g., fused-deposition modeling (FDM)) and stereolithography (SLA) have reliably achieved smaller feature sizes. Lower material cost in comparison to metal printing also makes these technologies an attractive alternative. However, without the functional properties of a metal, the utility of these parts is often restricted to a narrow range of applications.
Metallization of plastic surfaces can be aided by the initial step of plasma treatment on planar samples, but plasmas cannot uniformly react with finely detailed 3D-printed structures such as dense lattices. Strong chemical oxidants such as chromic acid can be used to assist in a chemical plating process but these can have adverse environmental consequences and are still not sufficient to adequately coat dense lattices.